Chemical and physical methods for the synthesis of magnetic nanoparticles for cancer detection and treatment often involve toxic chemicals, high cost and the formation of non-stable nanoparticles. This prompted the development of fundamental understanding of the synthesis of magnetic nanoparticles, which are biocompatible, cost effective, stable, localized and environmentally friendly in the presence of magnetotactic bacteria.
In this work, fundamental understanding of the underlying mechanisms involved in the formation of magnetic nanoparticles by magnetotactic bacteria are unraveled. Soil dwelling microbes that respond to magnetic pull were cultured in the presence of ferrous salts in a magnetic spirillum growth medium (MSGM). A comparative analysis was made whereby a positive control Magnetospirillum magneticum and an indigenous isolated strain were used in the biosynthesis of magnetic nanoparticles. The dependence of particle shape and size on pH and time, were elucidated using a combination of transmission electron microscopy (TEM) and UV-visible spectrophotometry. The implications of the results are discussed for the development of magnetic nanoparticles for the detection and treatment of cancer.
1.1 Background and Motivation
Nanotechnology has provides solutions to some critical problem in the areas of energy generation [1, 2], information storage , environmental remediation [4, 5] and biological application  to mention but a few. In the recent years, there has been increasing interest in the development of nanoparticles for potential and emerging applications in medicine . These include potential emerging applications in disease detection and treatment [8, 9], biological labelling , biosensors  and drug delivery .
In the case of magnetic nanoparticles (MNPs), there have been significant efforts to develop magnetic nanoparticles for application in cancer detection via magnetic resonance imaging (MRI)  and treatment by hyperthamia . In MRI, the current spatial resolution of detection is of the order of a few millimeters . MNPs have been produced largely from Iron, cobalt, iron oxide (Fe3O4) and Fe3CoO4 (Yang et al 2006). Their potential has also been explored for use as contrast enhancement agent during MRI of tumour tissue  and localized hyperthamia  during cancer treatment. Magnetic nanoparticles have been reported to have the ability of binding to drugs, proteins, enzymes, antibodies, or nucleotides and can be directed to an organ, tissue, cells or tumors using an external magnetic field or can be heated in alternating magnetic fields for use in hyperthermia.
Fe3O4 MNPs are heat-generating nanoparticles which have the ability to convert electromagnetic energy to heat energy. These MNPs have been found to be efficient in the detection and treatment of cancer by MRI and simple radiation therapy. In this case of radiation therapy, energy produced is used to destroy the cancer cells and reduce the size of tumours effectively when a cyclic external magnetic field is applied.
In most cases, there are several physicochemical methods that are used for the synthesis of MNPs. These include: microemulsion, sol-gel synthesis, hydrothermal reactions, flow injection synthesis, electrochemical synthesis, pyrolysis, laser pyrolysis, microwave assisted, carbon arc, combustion synthesis, vapour deposition and chemical co-precipitation method [7, 17]. However these synthesis methods often involve the use of toxic chemicals that can have harmful effects on the environment.
There is therefore a need for environmentally friendly methods for the synthesis of magnetic nanoparticles, that has stimulated the recent interest in the biological synthesis of magnetic nanoparticles from magnetotactic bacteria. There is also a need to understand the underlying mechanisms of magnetic nanoparticle formation in the presence of magnetotactic bacteria. To this end, most work in this field has been done in improving the biocompatibility of the materials, but only a few scientific investigations and developments have been carried out to develop a fundamental understanding of the synthesis of magnetic nanoparticles, which are biocompatible, cost effective, stable, localized and environmentally friendly in the presence of magnetotactic bacteria. The need to understand the underlying mechanisms involved in the formation of magnetite nanoparticles by these bacteria will contribute positively in improving the quality of magnetic particles, their size distribution, their shape and surface under certain preexisting conditions. This would lead to characterizing them to get a protocol for the quality control and commercialization of these particles in cancer detection and treatment.